The present invention relates to a method of forming tubular overwrappings from a heat-sealable material.
The invention finds advantageous application in the field of machines for overwrappings packets of cigarettes in transparent heat-sealable material, and whilst reference is made specifically herein to such machines, no limitation of scope is implied. Conventionally, the overwrapping devices used in such machines are of a type essentially comprising a wheel affording a plurality of peripheral pockets and an infeed station through which the pockets are indexed in succession by the wheel, each pocket pausing to receive a single packet of cigarettes together with a sheet of the overwrapping material. The sheet is folded into a "U" formation around the packet as the packet is directed toward the wheel. The packet is received by the pocket with the two longitudinal edges of the "U" profile projecting as flaps which are folded into overlapping contact and heat-sealed one to the other, thereby fashioning a tubular wrapping around the respective packet.
In the conventional overwrapping devices referred to above, still found in widespread use, the flap of material projecting from the rear edge of the peripheral pocket, in relation to the direction of rotation of the wheel, is flattened against the respective packet generally by means of a moving folder. The moving folder is located adjacent to the infeed station and typically includes a plate of curved profile which, once the packet and the enveloping sheet of material have been transferred to the corresponding pocket of the wheel, is made to traverse along the periphery, concurrently with the rotation of the wheel, moving from an at-rest position to a folding position over the pocket. As the wheel is indexed thereafter through a further step, during which the moving folder may also be returned to the at-rest position, the folded rear flap emerges from beneath the contoured plate, and the remaining forwardmost flap enters into contact with a fixed folder by which it is flattened over a corresponding portion of the rear flap.
Conventional overwrapping devices of the type thus briefly outlined have certain drawbacks, stemming mainly from the indexing movement of the wheel and, if applicable, from the return of the moving folder to the at-rest position, during which the rear flap of the overwrapping sheet tends to shift backwards, i.e. in the direction opposite to that (forward) of the fold. Such dragging of the rear flap both against the moving folder and against a portion of the fixed causes the initial crease in the rear flap to be lost.
The object of the present invention is to set forth a method of fashioning tubular overwrappings that will overcome the drawback described above.